1. Field of the Invention
This invention relates to oxygen scavengers useful in the polymerization of vinyl unsaturated monomers, oligomers, and polymers in the presence of oxygen.
2. Description of the Prior Art
Eickoff et al, U.S. Pat. No. 4,395,361, assigned to Proctor and Gamble Company, teach a class of oxygen-activated free radical polymerization catalysts comprising cobalt (II) compounds and certain autoxidizable cyclic hydrocarbons and benzaldehyde.
Eickoff et al also describe a method of catalyzing an oxygen-initiated free radical polymerization reaction using these catalysts. No other aldehydes than benzaldehyde are disclosed.
Gruber U.S. Pat. No. 4,017,652, assigned to PPG Industries, Inc., teaches oxygen inhibition of the photopolymerization of acrylic resins being reduced by employing a photocatalyst system containing an aromatic ketone and/or aromatic aldehyde photosensitizer of a certain type which promote polymerization through bimolecular photochemical reactions, and an aromatic ketone photoinitiator.
Petersen, U.S. Pat. No. 3,551,423, assigned to BASF, teaches production of certain amides by reaction of amides with formaldehyde and an appropriate CH-acid aldehyde and the use of the new amide products as textile finishes and as valuable intermediates for the production of amino aldehydes and aminocarboxylic acids, pharmaceuticals and aminoplasts. Peterson does not disclose utility of the aldehydes as oxygen scavengers, nor does he disclose the corresponding imines.
Collins et al, Reactions of UV curable Resin Formulations and Neat Multifunctional Acrylates II Photoinitiated Polymerization of Neat 1,6-hexanedioldiacrylate, Journal of Coatings Technology, Vol. 51, No. 648, January 1979, teach benzoin isobutyl ether photoinitiated polymerization of 1,6-hexanedioldiacrylate, and eliminating the inhibition by dissolved oxygen by the addition of N,N-dimethylaminobenzaldehyde and eosin-Y.
Imoto et al, Vinyl Polymerization. 364. Polymerization of Methyl Methacrylate Initiated with Benzaldehyde, J. Poly. Science: Polymer Chemistry Edition, 17:385-92 (1979) show an anaerobic initiation of the radical polymerization of methyl methacrylate with benzaldehyde. Oxygen scavenger activity is not needed in anaerobic reactions, and so Imoto et al is not pertinent to oxygen scavenging.
In recent years, certain vinyl monomer, oligomer, and polymer systems have been developed which have sufficiently high molecular weight and sufficiently low odor, volatility, and toxicity so as to be useful as non-volatile reactive components of high or 100% solids resin formulations which can be cured rapidly by free radical polymerization in the absence of oxygen, i.e. anaerobically, for example in radiation cure applications or in engineering adhesives where polymerization occurs between two substrates to be bonded. However, when cure of these vinyl unsaturated systems is attempted in the presence of air, i.e. aerobically, serious inhibition of free radical polymerization by oxygen at the air interface occurs. It is this problem to which the present invention is addressed.
It is an object of the present invention to provide a new class of highly efficient oxygen scavengers for use in compositions comprising at least one vinyl unsaturated monomer, oligomer or polymer. It is a further object of the invention to provide compositions comprising at least one vinyl unsaturated monomer, oligomer or polymer which have improved curing characteristics in the presence of oxygen.